Polyolefin polymers and polymer blends are known for their versatility and applicability in a wide variety of uses. In particular, many polyolefin polymers, including copolymers of propylene with other α-olefins such as ethylene, are well suited for use in applications requiring good stretchability, elasticity, and strength. Materials with good stretchability and elasticity are used to manufacture a variety of disposable articles in addition to durable articles including but not limited to incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. For clothing, stretchability and elasticity are performance attributes that allow the materials to provide a closely conforming fit to the body of the wearer.
While numerous materials are known to exhibit excellent stress-strain properties and elasticity at room temperatures, it is often desirable for elastic materials to provide a conforming or secure fit during repeated use, during extensions and retractions at elevated or depressed temperatures, or in automobile interiors during summer months. Elasticity at elevated temperatures is also important for maintaining tight tolerances throughout temperature cycles. In particular, elastic materials used for repeated wear clothing or garments must maintain their integrity and elastic performance after laundering.
Spandex, a segmented polyurethane urea elastic material, is currently used in various durable fabrics. For example, fibers made from Spandex have been used in launderable apparels, fabrics, durable and disposable furnishing, beddings, etc. Similar to conventional uncrosslinked polyolefin-based elastic materials, articles made from Spandex can lose integrity, shape, and elastic properties when subjected to elevated temperatures. Thus, Spandex is not suitable for many co-knitting applications with high temperature fibers, such as polyester fibers.
Propylene-based polymers having good elastic properties are known and have been used for stretchable clothing. See, for example, U.S. Pat. No. 6,525,157 and U.S. Pat. No. 6,342,565. U.S. Pat. No. 6,342,565, in particular, discloses a soft, set-resistant, annealed fiber comprising a blend of polyolefins. The blend has a flexural modulus less than or equal to 12,000 psi and includes from 75 to 98 wt % of a first polymer component and from 2 to 25 wt % of a second polymer component. The first polymer component is a propylene-ethylene polymer having at least 80 wt % propylene and up to 20 wt % ethylene, a melting point (Tm) by DSC in the range of from 25 to 70° C., and a heat of fusion less than 25 J/g. The second polymer component is a stereoregular isotactic polypropylene having a melting point by DSC of greater than 130° C., and a heat of fusion greater than 120 J/g. The fiber exhibits a resistance to set equal to or less than 80% from a 400% tensile deformation. The polyolefin blend is said to be substantially non-crosslinked.
U.S. Pat. No. 6,500,563 discloses blends of two different types of polypropylene, including blends made from a polypropylene having a Tm of less than 110° C. and propylene-ethylene copolymer that has isotactically arranged propylene derived sequences and Tm less than 105° C.
U.S. Publication No. 2006/0183861 discloses cross-linked elastomeric compositions, including blends made from a propylene-based polymer blended with at least one component selected from the group consisting of multifunctional acrylates, multifunctional methacrylates, functionalized polybutadiene resins, functionalized cyanurate, and allyl isocyanurate, and at least one component selected from the group consisting of hindered phenols, phosphites, and hindered amines. The blends are cross-linked by exposure to electron beam radiation.
Three component blends of isotactic polypropylene, impact modifying amounts of an ethylene-propylene based rubber or low density ethylene copolymer and a propylene-based elastomer as compatibilizer are described in EP 946640, EP 946641, EP 969043 and EP 1098934.
WO 04/014988 describes blends of isotactic polypropylene with non-functionalized plasticizers such as poly-alpha-olefins. WO 03/040233 also discloses two component blends with the isotactic polypropylene as the predominant, matrix phase and the propylene-based copolymer serving as an impact modifier.
EP 1003814 and U.S. Pat. No. 6,642,316 disclose two-component blends of small amounts of isotactic polypropylene and predominant amounts of an ethylene based elastomer. EP 0374695 discloses visually homogeneous two component blends however using 40 wt % or less of the propylene-based copolymer. WO 00/69963 describes films made of two-component blends with from 75 to 98 wt % of a propylene ethylene based elastomer having a heat of fusion of less than 25 J/g.
Other related references include U.S. Publication Nos.: 2006/102149; 2005/0107529; 2005/0107530; 2005/0131142; and 2005/0107534.
Many polyolefin blends such as those disclosed in the prior art are formed into pellets for intermediate storage purposes before being shaped into articles such as fibers, films, nonwovens, extruded coatings, and molded articles. Some of these compositions, however, are known to exhibit poor pellet stability over extended periods of time, leading to agglomeration of pellets and resulting in poor pourability and flowability of the pellets.
There is therefore still a need for new and improved propylene-based materials which exhibit good pellet stability while also displaying good stretchability and elasticity for use in a wide variety of applications.